1. Field
This invention relates to transport of substrates and, specifically, to high throughput transport of substrates from atmospheric into vacuum environment for fabrication of solar cells.
2. Related Arts
Vacuum transport of substrates has been used in the manufacture of semiconductors for many years. A typical loadlock device has one valve as entry port to receive wafers from atmospheric environment, and valve as one exit port for delivering wafers into the vacuum processing system. In many systems the entry port also used to return wafers to the atmospheric environment. In such systems, a robot arm positioned on the atmospheric side places the substrate inside the loadlock and, after vacuum is established in the loadlock, a robot arm positioned on the vacuum side of the system (e.g., a mainframe) fetches the substrate from the loadlock and places it in a vacuum processing chamber, e.g., a plasma chamber. Once processing is completed, the vacuum-side robot places the processed substrate in the loadlock, and, after establishing proper pressure, the atmospheric-side robot fetches the processed substrate out of the loadlock. While such an architecture works well for semiconductor processing, solar cell fabrication requires much higher throughput. For example, while semiconductor processing proceeds at a rate of around 60-100 wafers per hour, solar cell fabrication proceeds at the rate of 1500-2500 wafers per hour. Thus, a new loadlock architecture is needed to facilitate such high throughput.
Additionally, due to the high speed processing of solar cells, and the relative low cost of each individual cell as compared to a semiconductor substrate, wafer breakage is a relatively frequent and an acceptable event in solar cell fabrication, while it is not acceptable in semiconductor processing. Still, the system needs to be able to recognize and handle events of wafer breakage. This is especially the case where wafer breaks inside the vacuum environment, where no manual identification and handling of the broken wafer can be performed without breaking vacuum and disassembling parts of the system. Accordingly, improvements in systems for manufacturing of solar cells are needed to identify and handle wafer breakage.